1. Field of the Invention
This invention relates generally to refrigeration systems and more particularly, it relates to an apparatus and method for controlling continuously and discretely the speed of an indoor evaporator fan motor and the speed of the compressor as a function of the fan speed for regulating the dry bulb temperature and relative humidity of a conditioned space. The invention has specific applications in air conditioning systems and in reversible heat-pump systems operated in the cooling mode for cooling residential dwellings, small office buildings, mobile homes and the like.
2. Description of the Prior Art
In U.S. Pat. No. 3,324,672 issued on June 13, 1967 to W. L. Sones et al., there is shown an electronically controlled conditioning system having a computer unit and a comfort control programmer for controlling the power applied to a compressor motor and blower motor.
In U.S. Pat. No. 3,214,913 issued on Nov. 2, 1965 to D. J. Petranek, there is disclosed a refrigeration system wherein a compressor is driven by an internal combustion engine via alternating current generator. The combustion engine is designed to operate at two distinct and separate speed ranges. The generator is also arranged to drive a pair of electric motors coupled to respective fans. However, the fan for circulating air within the conditioned space is operated at substantially uniform speed.
In U.S. Pat. No. 3,487,655 issued on Jan. 6, 1970 to D. D. Dennis et al., there is disclosed a heat-pump system which includes a compressor driven by a turbine via an alternator-motor combination. The alternator portion is also utilized to drive the condenser and evaporator fan motors. The compressor and fans are all simultaneously regulated in response to variations in the speed of the turbine.
In U.S. Pat. No. 4,071,741 issued on Jan. 31, 1978 to B. C. Hall, there is shown and described a system for controlling the measured temperature during a sequence of time intervals in conformity with a sequence of selected reference temperatures. Each of the reference temperatures correspond to one of the time intervals.
In U.S. Pat. No. 4,090,116 issued on May 16, 1978 to D. L. Lippitt, there is disclosed a motor control system which includes a data processor adapted to control the speed of an electric motor in response to input variables to the processor.
Heretofore, refrigeration systems have been operated on the basis of an on and off cycling of the compressor in response to measured temperatures which resulted in an inefficient operation due to substantial lag or overshoot of the desired temperature in the conditioned space. Further, this type of on and off cycling causes energy to be wasted due to the transients encountered during start-up and shut-down. There have been attempts to improve the efficiency of the system by operating the compressor more or less continuously. However, it has been discovered that in order to minimize energy consumption there should be a regulation of the speed of the evaporator fan motor in response to the load conditions and the speed of the compressor should be made as a continuous and discrete varying function of the fan speed. Thus, it would be desirable to provide an apparatus and method for controlling continuously and discretely the compressor speed as a varying function of the evaporator fan speed which is dependent upon the load conditions.